Harknessiaceae Crous, Persoonia, Mol.Phyl. Evol. Fungi 28: 55 (2012)

Index Fungorum number: IF564740; 69 species.

Saprobic or pathogenic on leaves or twig litter. Sexual morph: Ascomata perithecial, solitary or aggregated, immersed, globose, coriaceous, brown, ostiolate, papillate. Papilla emergent to depressed, comprising 3–5 layers of brown-walled cells of textura angularis. Paraphyses septate, branched. Asci 8-spored, unitunicate, cylindrical to clavate, short pedicellate, with J-, apical ring. Ascospores uniseriate to biseriate, hyaline, ellipsoid to fusoid, aseptate, thick-walled, guttulate, smooth-walled. Asexual morph: Coelomycetous. Conidiomata eustromatic, pycnidial, scattered or aggregated, immersed, globose, coriaceous, with single or several locules, dark brown to black, ostiolate. Peridium comprising thin-walled, almost hyaline to brown cells of textura angularis.
Ostiole wide, centrally located, surrounded by brown cells. Conidiophores lining the inner cavity, or reduced to basal layer; sometimes septate, branched; sometimes reduced to conidiogenous cells. Conidiogenous cells holoblastic, integrated, lageniform, subcylindrical to cylindrical, hyaline to pale yellow, smooth, producing macroconidia and sometimes microconidia from same conidiogenous cell; sometimes proliferating sympodially one or several times. Macroconidia with a basal appendage, hyaline when young, brown at maturity, unicellular, although basal appendage separated by a thick, smooth-walled septum, with or without light and dark longitudinal bands, sometimes longitudinally striate, guttulate; basal appendage cellular, cylindrical to subcylindrical, hyaline, thin-walled, devoid of contents; apical appendage present or absent, if present elongate. Microconidia hyaline, oval to ellipsoid, aseptate, smooth-walled (adapted from Senanayake et al. 2018).

Type genus – Harknessia Cooke

Notes – Harknessiaceae was initially proposed by Castlebury et al. (2002), subsequently formally introduced by Crous et al. (2012d) to accommodate Harknessia with their wuestneia-like sexual morphs. Species of Harknessiaceae have pycnidial conidiomata with brown, furfuraceous margins, brown conidia with hyaline, tube-like basal appendages, longitudinal striations, and rhexolytic secession (Crous et al. 2012d, Senanayake et al. 2018). Harknessiaceae species seem to have a cosmopolitan distribution, since they have been recorded worldwide, and are commonly associated with leaf spots and branches of various hosts (Sankaran et al. 1995, Farr & Rossman 2019). They have also been recorded as endophytes and saprobes in leaves and twigs of various angiosperm plants and noxious weeds (Crous et al. 2012d). LSU analysis supports this family which was earlier placed in Diaporthales (Crous et al. 2012d). Crous et al. (2012d) introduced six novel species of Harknessia on Eucalyptus and supported by a multi-gene analysis (ITS, calM and tub2) for these species.

Ecological and economic significance of Harknessiaceae
Most members in the family are associated with leaf spots, leaf tip-dieback or leaf scorch and stem cankers and they are suspected to be pathogens mainly in Eucalyptus (Crous et al. 1989, Marincowitz et al. 2008). However, many species have been isolated from asymptomatic plant tissues and are assumed to be saprobes. Therefore, their pathogenicity is still ambiguous. Normally they are species with less economical significance (Park et al. 2000).